Milestone: 400 Parts Per Million

“A lot of what’s known about carbon dioxide in the atmosphere can be traced back to a chemist named Charles David Keeling, who, in 1958, persuaded the U.S. Weather Bureau to install a set of monitoring devices at its Mauna Loa observatory, on the island of Hawaii. By the nineteen-fifties, it was well understood that, thanks to the burning of fossil fuels, humans were adding vast amounts of carbon to the air. But the prevailing view was that this wouldn’t much matter, since the oceans would suck most of it out again. Keeling thought that it would be prudent to find out if that was, in fact, the case. The setup on Mauna Loa soon showed that it was not.

”Carbon-dioxide levels have been monitored at the observatory ever since, and they’ve exhibited a pattern that started out as terrifying and may be now described as terrifyingly predictable. They have increased every year, and earlier this month they reached the milestone of four hundred parts per million. No one knows exactly when CO2 levels were last this high; the best guess is the mid-Pliocene, about three million years ago. At that point, summertime temperatures in the Arctic were fourteen degrees warmer than they are now and sea levels were some seventy-five feet higher.“

-- Elizabeth Kolbert, in her piece, ”Lines in the Sand," mostly about whether Pres. Obama will approve the construction of the Keystone XL pipeline from Alberta, Canada to Nebraska. Her arguments against, including an explanation of what tar-sands oil is, start in the 7th paragraph.